There’s two ways of hooking up your speakers to your soundcard: Analog and Digital. Analog uses the standard stereo audio jacks you’ll see on any soundcard, just more of them. Digital uses either a TOSLINK Optical output or a coaxial digital output. With digital output, the audio is sent to a reciever, where it is decoded and sent to the individual speakers. With analog output, audio is decoded by the soundcard and sent directly to the speakers. In theory, there shouldn’t be any quality difference between them. In reality, the quality of the Digital to Analog Converters on the soundcard decide whether analog output sounds better or worse than digital output.
Standard DVD Audio is in Dolby Digital or DTS, and is 5.1 surround (Center, Front-Left, Front-Right, Surround-Left, Surround-Right, Low Frequency Effect(LFE, the subwoofer)). Some DVDs use the newer Dolby Digital EX format which offers 7.1 surround sound (Center, Front-Left, Front-Right, Surround-Left, Surround-Right, Rear-Left, Rear-Right, LFE). I think DTS also has a 7.1 surround format, but I’m not sure what its called or if its widely in use.
As for soundcards:
Tech-Report just reviewed the M-Audio Revolution 7.1 soundcard and were very impressed with it, preferring it over the Creative Audigy 2. This card features analog 7.1 output, as well as coaxial digital output. It costs about $90 retail.
As for Creative’s cards, the Audigy 2 is their current model. The Platinum version uses gold-plated connectors, and has an extra “Audigy2Drive” that goes in a 5.25" drive bay, offering extra connectors and other frills such as volume control knobs, TOSLINK optical input and output, RCA inputs, and a remote control.
Overall, if I were buying a soundcard now I’d probably go with that M-Audio Revolution 7.1 card that Tech-Report reviewed. I would personally avoid Creative, as they’ve done some unsavory things recently (The Soundblaster Live! has the annoying habit of corrupting your harddrive regularly, the Audigy was advertised as 24-bit when it wasn’t, and they charged for drivers updates needed to get their soundcards to function, instead of putting them on their website). Unfortunately, I haven’t kept up with the speaker market so I can’t give you any specific recommendations, but a good set of 7.1 analog speakers would seem to be your best bet.